1. Field of the Invention
The present invention relates to a centrifugal fan having a substantially cylindrical housing in which an impeller, a motor for driving the impeller and a substantially disk-like circuit board are disposed coaxially in an accumulated manner. In particular, the present invention relates to a structure for enhancing an effect of cooling a self-heating electronic component mounted on the circuit board.
2. Description of the Related Art
A cooling fan, which has a small dimensions particularly in the axial direction for a use in an electronic device, usually includes an impeller, a motor for driving the impeller and a substantially disk-like circuit board that are disposed coaxially in an accumulated manner inside a housing. On the circuit board, there is mounted a self-heating electronic component such as an integrated circuit for driving and controlling the motor. As a rotation speed of the impeller increases, a heat value of the integrated circuit also increases. In order to obtain sufficient blowing performance, it is necessary to enhance a radiation effect of the integrated circuit. Therefore, in a conventional structure, an air flow generated by rotation of the impeller is partially utilized for enhancing the radiation effect of the electronic component such as an integrated circuit.
This type of cooling fans can be roughly divided into axial fans and centrifugal fans. In an axial fan of a conventional example, the rotating impeller takes air from one side in the axial direction, and the air goes out from the other side in the axial direction. In this conventional example, The circuit board is disposed at one side in the axial direction of the impeller (an inlet side or an outlet side), and a radiator film (a conductive pattern) is arranged at the perimeter of the outer periphery of the circuit board, which is connected to a heat sink terminal of the integrated circuit. Then, a part of the air flow generated by rotation of the impeller cools the radiator film, so that a cooling effect of the integrated circuit can be enhanced.
In an axial fan of another conventional example, air is taken in through an inlet arranged at one side or inlets arranged at both sides in axial direction and sent in the circumferential direction inside the housing, and the air goes out radially (centrifugally) from an outlet disposed on the circumference surface of the housing. In this conventional example, a rectangular box-like odd housing is used, and a self-heating component is arranged at a corner of its inner space deviated from the outer rim of the impeller. Note that the circuit board also works as a wall on one side of the housing in the axial direction, and the self-heating component is mounted at a corner of the circuit board having a rectangular contour so that the structure described above is realized. A part of the air flow running through the inside space of the housing in the circumferential direction cools the self-heating component.
Although the structure described above is known as a structure for cooling a self-heating component mounted on a circuit board of a centrifugal fan, this structure has a disadvantage as follows. Firstly, if a size of the circuit board that constitutes a side face of the housing increases, the circuit board is required to have an opening corresponding to an air inlet that may be arranged on the side face. Therefore, a wasted part of the circuit board increases resulting in a disadvantage in cost. In addition, a normal centrifugal fan uses a substantially cylindrical housing whose inner space has a cross section increasing gradually in the circumferential direction toward the air outlet. However, the structure of the conventional example described above uses a rectangular box-like odd housing. Therefore, the cross section of the inner space (air flow channel) changes in the circumferential direction, so it is difficult to obtain a smooth blowing performance. In addition, since the self-heating component is disposed in the air flow channel, air turbulence tends to occur resulting in a problem of a deficient blowing performance or a noise.